Process for continual stretch forming



July 30, 1968 E. R. BODNAR 3,394,573

PROCESS FOR CONTINUAL STRETCH FORMING Filed June 20, 1966 5 Sheets-Sheet 1 FIG.

INVENTOR:

ERNEST ROBERT BOD/VAR Car/and &' Woman July 30, 1968 E. R. BODNAR PROCESS FOR CONTINUAL STRETCH FORMING 3 Sheets-Sheet 2 Filed June 20, 1966 STRAIN, INCHES PER. INCH INVENTOR.

ERNEST ROBERT BOD/VAR 6auanagA 8 Woman July 30, 1968 E. R. BODNAR 3,394,573

PROCESS FOR CONTINU TTTTTTTTTTTTTT NG Filed June 20, 1966 5 Sheets-Sheet 5 '0 '1!!! III 1,111,111

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,IIIIII FIG. 8 9

INVENTOR:

ERNEST ROBERT BODNAH Cauanag & Woman United States Patent 3,394 573 PROCESS FOR CONTINUIAL STRETCH FORMING Ernest Robert Bodnar, 29 Blackdown Crescent, Islington, Ontario, Canada Filed June 20, 1966, Ser. No. 558,724 11 Claims. (Cl. 72196) This invention relates to improvements in methods for stretch forming metals in a continual process.

conventionally the forming of metal sheets into Various shapes is performed by a drawing technique or by stretching the metal to provide forms. In deep drawing of metal certain limitations are imposed upon the design of shapes by the inherent properties of the material and in many cases in order to provide a deep draw such as a comparatively deep dish within a metal sheet, it is usual to resort to progressive dies which form in two or more operations the completely drawn part. The concept of progressive dies is also utilized in forming complex shapes from strip material, the strip normally being passed through two or more dies arranged in a row, the forming of the part taking place progressively until the completed shape has been formed.

In some instances the technique of stretch forming is used wherein a sheet of material is stretched over a male die until permanent deformation of material occurs at which time tension in the material is released, the part then maintaining the shape of the die.

While the multiple progressive die method solves problems relating to the formation of complex parts, and while stretch forming techniques are utilized in providing comparatively deep forms or draws in material, neither process has heretofore been effectively utilized in continual forming operations of strip material.

By resort to the present invention however, there is provided a process for the deep drawing of metal strip to provide continual draws along the length of the strip is provided and the invention accomplishes this object by providing a process to produce similar stretch forms continually in a metal strip and utilizing steps of first passing in tension the strip between a pair of tensioning roller sets to continuously tension the strip below the yield point of the metal, and then providing a pair of rotating died members including male and female halves interspaced between the roller sets and adapted to rotatably close on the strip, the die halves stretching the tensioned strip to provide similar forms along the length of the strip.

Other objects and features of the invention will be apparent from the following detailed description and accompanying drawings in which like numerals refer to like parts throughout the various views and diagrams.

In the drawings:

FIGURE 1 is a side elevation partly in section of apparatus suitable for carrying out the present invention;

FIGURE 2 is a perspective view of strip material formed by the apparatus according to the present invention;

FIGURE 3 is a perspective view partly in section illustrating the metal strip formed by the apparatus;

FIGURE 4 is a chart illustrating certain aspects of the present process; and

FIGURES 5 to 8 inclusive illustrate the stretch forming of the metal strip according to the present invention, the four views in section illustrating four stages during the metal stretching.

In FIGURE 1 apparatus indicated generally as 10' is shown and comprises a first tensioning roller set assembly as at 11, a second tensioning roller set assembly indicated at 12 and a rotating die member assembly interposed between the assemblies 11 and 12 indicated as 13. The direction of travel of the strip 14 is as indicated by the arrow 15, the metal unwinding from the roll 16.

A predetermined stretch is put on the metal strip at 17 between the roller assemblies 11 and 12 whereby the strip being fed continuously through the apparatus is stressed in tension below the yield point of the particular metal of the strip. Upon passing between the die members such as for instance, the upper female die member 18 and the lower male die member 19 the strip 17 is provided with a similar number of stretch forms as at 20 along the length thereof.

The first tensioning roller set assembly 11 comprises an end mounting frame 22 supporting an upper roller member 23 and a lower roller member 24 thereon, there being provided in practice a pair of end frames 22 but only one being shown in this drawing. An adjustment screw 25 acts through the slide mechanism 26 to apply pressure on roller 23 to bias same into contact with the strip 14 and to be held tightly onto the lower roller 24. In a similar manner tensioning roller set 12 is provided with the upper roller 27 and lower roller 28 also provided with the adjustment 29 working through the slide 30 to apply pressure on roller 27 to bias same downwardly onto the strip as at 31 and thus to be held tightly on the lower roller 28.

It will be noted that the tensioning roller set 12 has the upper roller 27 and the lower roller 28 formed to conform with the configuration of the metal strip depending upon the configuration given by the rotating die members 13. Thus in the configuration illustrated in FIGURE 1 and FIGURE 2 allowance is made in the rotating tensioning rollers 27 and 28 to conform to the forms 20 as well as the longitudinal forms along the length of the metal strip. It will be understood that the configuration of the surface of upper and lower rollers 27 and 28 would be varied to suit the form of the strip being made according to the form taken by the strip after it passes through the rotating die members.

By suitably altering the compression pressure on the respective rollers 27 and 23 and by providing suitable drive mechanisms for the roller sets the amount of tensioning between the individual roller set assemblies 11 and 12 can be controlled. It should be understood that the various mechanisms such as gears and motors required for driving the rollers is well known in the art and for this reason is not illustrated in detail in the drawings. As is common with many types of rolling mills which roll metal strip into shapes having continuous cross sectional configurations, a number of the frames 22 are provided along the rolling line to support the various types of roller dies used. For this reason the present invention can be utilized in a conventional type of roller die machine, the process of the present invention being as herein described and illustrated.

The rotating die assembly 13 operates to stretch the metal beyond the yield point to so deform the metal to provide the individual stretch forms 20. Thus while the metal between the tensioning roller assemblies 11 and 12 is held in tension below the yield point, the metal is in fact stretched beyond the yield point while passing through the rotating die members 18 and 19.

In FIGURE 2 a typical section of strip metal formed according to the present invention is shown wherein the metal is provided with the side channels as at 32 and 33 having interconnecting cross channels 34. By suitably fastening a second formed piece as at to the upper portion an assembly suitable for heat transfer purposes, such as for instance for use in heating systems, is provided. It will be appreciated that in many types of heating systems such a heat exchange unit may be provided of a width of say perhaps ten inches and of length up to several feet to meet individual heating requirements in baseboard type installations. For this reason the method of the present invention provides means whereby the required sections can be produced in a continual process without resort to comparatively expensive dies and comparatively massive stamping machines which ordinarily would be required to produce such sections in length of several feet.

Referring to FIGURE 3 further details of apparatus suitable for carrying out the process according to the present invention are illustrated. The view shows the tensioning roller set assembly 11 in part which comprises the upper roller 23 and lower roller 24 which are adapted upon movement of the mechanism driving the rollers to form the edges as at 36 of the strip 14 partially downwardly, the tensioning roller set 11 thus acting also as a partial forming roller set. The rotating die members upper die member 18 and lower die member 19 which are rotatably supported in end assemblies 22 and provided with a slide 37 similar to the slides 26 and 36 which in turn is operated by means of the screw device 38 as shown in FIGURE 1, are provided with cavities as at 39 on member 18 thereabout. The lower die member 19 is similarly provided with a plurality of rams 40 thereabout which match the cavities 39 whereby the cross channels 34 are formed in the strip 17 as it passes this portion of the process. From this it will be seen that firstly the strip 14 is partially formed along the edges to provide the strip 17 whereafter the completion of the forming is done by the rotating die members. In order to maintain the die members in alignment the gears 41 and 42 are utilized between the upper and lower die members 18 and 19 respectively. In this case the lower die member 19 is the driving die receiving its drive through the shaft 43 and the key 44.

In FIGURE 4 a stress-strain curve is shown, this being a typical curve for annealed low-carbon steel which is a common material used for manufacturing stretched or drawn parts. The curve shown is a straight line up to the point P1 and this portion represented by A is the range of the elastic limit of the material. The point P2 represents the yield point of the metal with the portion C representing the area of permanent deformation. Normal flexure takes place in the range of A while the range C is the range normally employed for deep drawing operations.

However, in the area represented by B metal can be worked by various means to produce forms therein. This is the range wherein normal stretching operations are performed where the metal is permanently deformed but not so vigorously as would take place in the higher ranges as at C. Thus the process according to the present invention entails stretching the metal in the range A below the yield point P2, whereafter permanent deformation is obtained by stretching the metal in the range B. It should be understood that the ranges shown are given as indications only and to illustrate the process according to the present invention in terms for a common metal. It should also be noted that due to the comparative flattening out of the curve in the region of the point P2 a metal flows into permanent deformation with comparatively little stress being applied and thus the metal is quite ductile in this range. Thus by pre-stretching the metal up into the range towards P2 but still within the range A forming and deformation of the metal during the stretching takes place more easily than would otherwise be the case should a simple stretch forming be performed.

The stretch forming process for a single stretched form according to the present invention is depicted in FIG- URE'S 5 to 8 inclusive. The figures are sections through the mating surfaces of the upper and lower rotating die members 18 and 19 having the cavities 39 and the rams 40 respectively. For ease of explanation one ram member 40 has been designated with an X in order that a stretching operation can be followed from beginning to completion.

In FIGURE 5 the direction of rotation of the upper and lower die members is as indicated by the appropriate arrow and the direction of travel of the strip metal therebetween is as noted by the arrows. The X-ram 40 is shown just touching the underside as at 45 of the strip 17 the side flange 32 already being held within the sides of the die members 18 and 19.

In FIGURE 6 the X-ram 40 has been rotated until the channel 34 has been partially formed in the strip 17 and it will be noted that the corner 46 of the upper die member 13 along one edge of the cavity 39 is pinching the metal against the X-ram 40 to cause permanent deformation in this area.

In FIGURE 7 the die members 18 and 19 have rotated until the cavity 39 is vertically above the X-ram 40 and it will be seen that clearance exists between the upper and lower die members at the corner position 47. Also it will be seen that a similar clearance exists at the position 48, however at this position the material of the strip 17 has not yet been pinched into final position.

In FIGURE 8 the corner 49 of the upper die member 18 is shown pinching the strip 17 against the X-ram 40 to provide a permanent deformation similar to the deformation shown in FIGURE 6 at the corner 46. Also it will been in FIGURE 8 that the succeeding ram 40 is beginning to form the channel 34 in the strip 17 this position being slightly more advanced than the X-ram 40 shown in FIGURE 5.

As has been stated the operation of the present invention is carried out on a metal forming line similar in construction to a conventional roll forming line. In order to maintain a predetermined tension on the metal strip as it is fed into the rotating die and after it leaves these rotating die members resort may be had to well known techniques. Thus by altering the relative diameters of the tensioning roller sets, that is by making the first tensioning set of a diameter less than the second tensioning roller set and by driving both sets at the same speed of revolution, the metal between the respective sets will be placed in tension. In some cases it may be desirable to drive one roller set at a slightly greater rate than the previous roller set in order to effect tension, in either case the tensioning of the metal strip being due to a slipping grip on the metal by one or both sets of tensioning rollers.

The frames 22, a pair of such frames being provided for each set of rollers, are normally mounted to either side of the metal forming line and as is common with such prior types of machines the rollers are adjustably positioned therein, being suitably driven by gears connected to a main power source. Individual biasing means in the form of the springs 26 as shown in FIGURE 1 permit the variation in the contact pressure holding the metal strip between a particular set of rollers, this variation in pressure enabling the material passing therethrough to slip more or less thus to change the amount of tension applied to a strip between a particular pair of roller sets.

From the foregoing it will be seen that the present invention provides a process for forming similar stretch forms continually in a metal strip and does so by providing a tension in the metal strip below the yield point of the metal material and then stretch forming the individual forms by permanent deformation of the material locally. By applying the pre-stress to the metal strip as it passes between the roller stations the permanent deformation to provide the stretch forms is more easily accomplished than by normal stamping or deep drawing means. Since the metal flows more easily while in the prestressed condition, wrinkling and tearing of the metal is avoided.

It is to be particularly noted that during the initial stage of the forming of each form by the male die 49, that is to say during the transition from FIGURE 5 to FIGURE 7, the metal '17 is in fact stretched between the male die 40 on the one hand and the first tensioning roller set 23 and 24 on the other in progressively decreasing increments. Thus while deformation takes place mostly in the area of die 40, a certain amount of stretch takes place along the length of the strip toward the roller set 23 and 24.

It should also be noted that various other forms can also be produced according to the present process and that the particular form shown is done so by way of preferred example only. Thus individual separate dishes have been formed by resort to the process and it is contemplated that various other forms and combinations thereof can also be produced by the present process.

It should be further understood that although specific embodiments of the invention have herein been described and illustrated, the invention also contemplates such variations as may fall within the scope of the appended claims.

Bibliography The following published works may be referred to for definitions of terms used in the foregoing disclosure.

Metals Handbook, 1948 edition, published by the Amercan Society for Metals, 7301 Euclid Ave., Cleveland, Ohio.

Modern Metallurgy for Engineers, by F. T. Sisco, Pitman Publishing Corporation, 1941, New York, N. Y.

Websters Dictionary of Synonyms, G. & C. Merriam Co., published by George Banta Co., 'Inc., Wisconsin.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for providing stretched forms continually in a strip of selected metal of predetermined thickness and comprising the steps of: continuously passing in tension said strip at a predetermined unvarying speed between first and second tensioning roller sets to continuously stress said strip at a value below the yield point of the metal; and, progressively rotatably closing rotating mating male and female die members spaced apart a predetermined distance from one another in excess of the thickness of said metal strip and located between said tensioning rollers sets, the male and female die members stretching said forms along the length of said strip.

2. A process as claimed in claim '1 wherein the metal used is mild steel.

3. A process as claimed in claim 1 including the step of providing at least one continuous lengthwise form along said strip to interconnect said stretched forms.

4. A process as claimed in claim 1 including the step of providing a pair of continuous for-ms along both edges of said strip, said continuous forms being rolled in part at least by the first of said tensioning roller sets, whereby the gripping effort of said tensioning rollers is increased to more readily stretch said strip, said continuous forms providing interconnecting means between said stretched forms.

5. A process for providing stretched forms continually in a pretensioned strip of selected metal of predetermined thickness and width comprising the steps of: gripping the unformed strip across its full width between a first tensioning roller set, said set being driven at a predetermined peripheral speed; progressively rotatably closing rotating mating male and female dies on a portion only of said strip at a distance spaced from said first roller set thereby stretch forming a series of spaced forms in said portions of said strip, said portion being of a reduced width in relation to said strip; gripping that other portion of said strip remaining unformed between a second tensioning roller set said formed portion of said strip being free of engagement by said second tensioning roller set, said second set being driven at a peripheral speed in excess of that of said first tensioning roller set thereby to tension said strip therebetween to a value just below the yield point of the metal; said rotating male and female die members being driven at a speed intermediate that of said first and second tensioning roller sets.

6. A process for providing stretched forms continually in a predetermined strip of selected metal of predetermined thickness and width comprising the steps of gripping the unformed strip across its full width between a first tensioning roller set, said set being driven at a predetermined peripheral speed; progressively rotatably closing in sequence pairs of rotatably mating male and female die members on said strip, said male die member gradually progressively folding a portion of said strip around said male die member and into said female member and stressing said metal between itself and said first tension roller set to a value in excess of the yield point of the metal thereby stretching said metal in progressively decreasing increments from said male die member to said first tension roller set and stretch forming said metal to conform to said die members; gripping that other portion of said strip remaining unformed between a second tensioning roller set said formed ortion of said strip being free of engagement by said second tensioning roller set, said second set being driven at a peripheral speed in excess of that of said first tensioning roller set thereby to tension said strip therebetween to a value just below the yield point of the metal; said rotating male and female die members being driven at a speed intermediate that of said first said second tensioning roller sets.

7. Apparatus for providing stretched forms continually in a metal strip and comprising; a pair of tensioning roller sets, each pair having at least two rollers for passing the metal strip under pressural contact therethrough; means for providing different surface speeds for both said roller sets to maintain a predetermined tension in the strip between said roller sets at a value below the yield point of the metal; a pair of rotatable, mating die members having ram members iusertable within cavities and closeable on the strip in tension; and means for driving said rotatable die members to close on and stretch the metal beyond the elastic limit to provide stretched forms continually along the metal strip.

8. Apparatus as claimed in claim 6 wherein at least one of said roller sets is provided with means for forming at least one lengthwise form along the strip to interconnect said stretched forms.

9. Apparatus for providing stretched forms continually in a strip of selected metal and of predetermined width, and comprising: a first tensioning roller set having a gripping width not less than the width of the metal strip; means for driving said first tensioning roller set at a predetermined peripheral speed; a second tensioning roller set having a gripping configuration to match at least in part the configuration of said formed strip; means for driving said second tensioning roller set at a pehipheral speed greater than that of said first tensioning roller set; mating male and female die members rotatably supported between said first and second tensioning roller sets; and, means for driving said male and female die members at a peripheral speed between that of said tensioning roller sets, whereby the metal strip is stretched between said tensioning roller sets to be stressed at a value below the yield point of the metal, the mating die members deforming the strip to provide the stretched forms along the strip.

'10. Apparatus as claimed in claim 9 wherein said male die member is provided with a plurality of similar rams about the periphery to mate with a plurality of cavities References Cited about the periphery of said female die member, said rams and cavities being of a width less than the width of said UNITED STATES PATENTS strip. 804,512 11/1905 Witt 72-16 8 11. Apparatus as claimed in claim 9 wherein said first 5 2,903,039 9/ 1959 Raynes 72166 tensioning roller set is provided with means at the edges 3,123,905 3/ 1964 Thomas 72-196 thereof for forming at least one lengthwise form along 3,172,450 3/ 1955 HOCkmaIl 6t 81 7 168 X said strip to interconnect the individual forms provided by said rotating male and female die members. MILTON MEHR: Primary Exammer- 

1. A PROCESS FOR PROVIDING STRETCHED FORMS CONTINUALLY IN A STRIP OF SELECTED METAL OF PREDETERMINED THICKNESS AND COMPRISING THE STEPS OF: CONTINUOUSLY PASSING IN TENSION SAID STRIP AT A PREDETERMINED UNVARYING SPEED BETWEEN FIRST AND SECOND TENSIONING ROLLER SETS TO CONTINUOUSLY STRESS SAID STRIP AT A VALUE BELOW THE YIELD POINT OF THE METAL; AND, PROGRESSIVELY ROTATABLY CLOSING ROTATING MATING MALE AND FAMALE DIE MEMBERS SPACED APART A PREDETERMINED DISTANCE FROM ONE ANOTHER IN EXCESS OF THE THICKNESS OF SAID METAL STRIP AND LOCATED BETWEEN SAID TENSIONING ROLLERS SETS, THE MALE AND FEMALE DIE MEMBERS STRETCH. ING SAID FORMS ALONG THE LENGTH OF SAID STRIP. 